The invention relates to an aircraft radar antenna of the type having a directional pattern including a sharply focused principle lobe.
Modern aircraft pulse radar systems employ various pulse repetition frequencies (PRF) for target detection in the air-to-air operating modes. In the mode operating with a high PRF (HPRF), it is possible to unequivocally determine the velocity of a target, in the mode operating with a low PRF (LPRF) the distance of the target. The range in these operating modes is limited substantially by the average radiated HF power. In the mode operating with medium PRF (MPRF), target distance as well as target velocity can be determined but the result is ambiguous. The ambiguity can be resolved by changing the PRF and linking the results from measurements with different (medium) PRF's, e.g. according to the "Chinese remainder" method. In the mode operating with medium PRF, the range is limited primarily by ground clutter received by the antenna side lobes and is reduced, for example, compared to the HPRF mode which only furnishes the velocity of the target, by about 40%.
This loss of rang in the MPRF mode operation is particularly serious when considering the fact that the MPRF mode furnishes distance and velocity of the target in look-up and look-down situations under almost all target aspect angles.